1. Field of the Invention
The present invention relates to a pressure measuring module for detecting pressure of air within a tire of a vehicle, and a tire pressure monitoring system having the pressure measuring module.
2. Description of the Related Art
It is necessary that pressure of air within a tire of a wheel assembly attached to a car or the like be maintained to a predetermined level (e.g., approximately 220 kPa when the tire is used for a typical car) in order to maintain riding comfort and the fuel efficiency of the vehicle and prevent the tire from being damaged. In recent years, a system (tire pressure monitoring system (TPMS)) for measuring pressure of air within a tire and providing a warning upon a reduction in the pressure has attracted attention. Especially, the US law obliges users to place a TPMS in their vehicles.
Some of TPMSs respectively have a tire pressure measuring module (hereinafter, referred to as a pressure measuring module) attached to each wheel assembly and a pressure monitoring device attached to a vehicle, and are each designed to monitor pressure of air within a tire of each wheel assembly. The TPMSs has two types of information associated with each other: information on identifications that are respectively specific to the modules and transmitted from the modules; and information on the positions of the wheel assemblies to which the modules are respectively attached. The two types of information are registered in the pressure monitoring device. The TPMSs monitors pressure of air within each tire based on the information. In some of those TPMSs used in a process of assembling a vehicle or in a repair shop, dedicated terminal reads the information on the identification of the pressure measuring module from a barcode attached to the wheel assembly, and the pressure monitoring device receives the read identification information through a wired line from the dedicated terminal and registers the received identification information therein (refer to, for example, JP-A-2004-9859).
A pressure measuring module used in such a technique is provided in a tire in many cases. In general, a tire has a wire (bead wire) made of steel, and a wheel is made of metal. The inside of the tire attached to a rim of the wheel is electromagnetically shielded. When the pressure measuring module is provided in the tire, a radio wave transmitted from the pressure measuring module may be affected by the tire and the wheel and attenuated. As a technique for increasing the intensity of a radio wave received by a pressure monitoring device from a pressure measuring module, a receiving antenna of the pressure monitoring device, which is provided near a wheel assembly, has been disclosed (refer to, for example, JP-A-2003-165313).